Question

I can’t understand how to get the google closure compiler for javascript to properly recognize properties of a constructor. For example, in the code below, I don’t know what type to give ‘cls’ in line 27 so that the compiler does NOT produce the following (erroneous in my opinion) error:

foo.js:29: WARNING – Property say never defined on cls
cls.say();
^

From reading the documentation it seems that I should be doing it as I do in 25. Can someone help please? Thanks,

 1  /**
 2   * @interface
 3   **/
 4  function Sayer() {}
 5  Sayer.prototype.say = function() {};
 6  Sayer.say = function() {};
 7  
 8  /**
 9   * @constructor
10   * @implements {Sayer}
11   **/
12  function A() {}
13  A.say = function() { console.log('A factory'); };
14  A.prototype.say = function() { console.log('Am an A'); }
15  
16  /**
17   * @constructor
18   * @implements {Sayer}
19   **/
20  function B() {}
21  B.say = function() { console.log('B factory'); };
22  B.prototype.say = function() { console.log('Am an B'); };
23  
24  /**
25   * @param {function(new:Sayer)} cls
26   **/
27  function makeSayer(cls) {
28      var obj = new cls();
29      cls.say();
30      obj.say();
31  }
32  
33  makeSayer(A);
34  makeSayer(B);

Answer 1

“Sayer.say” on the interfaces is ignored.

Are you trying to prepare this for Closure’s advanced mode? In advanced mode “A.say” and “B.say” are renamed to “A$say” and “B$say”, the type check expects this and complains about it appropriately (there won’t be a method A.say).

You can avoid collapsing by have it added by it indirectly:

function addSay(sayer, fn) {
  sayer.say = fn;
}

I suppose you could avoid the type warning by adding a line like:

Function.prototype.say;

But I’m not sure you this is what you want.

You can avoid the hassle and add it to the prototype and call that instead:

A.prototype.classSay = function () {};